Thursday, March 29, 2007

Imagine... shedding pounds simply by spending more time in never-neverland. Sounds like something out of a late-night infomercial.

But two studies show a striking connection between amount of sleep and levels of appetite-regulating hormones in the body. The findings suggest that chronic sleep deprivation could be making you fat.

American adults have cut their average nightly sleep time by nearly two hours in the last 40 years. And while we've lost sleep, we've gained weight: In 1960, only one out of four adults was overweight, and one out of nine was considered obese. Now, two out of three adults are overweight, and nearly one out of three is obese.

Previous research had shown an association between shorter sleep time and higher body mass index, but no one knew why, says Dr. Shahrad Teheri, an endocrinologist at Bristol University, and lead author of one of the two studies.

He and his colleagues used data from the Wisconsin Sleep Cohort, which has tracked the sleep habits of over 1,000 volunteers for 17 years. They found that those people who slumbered (on average) five compared to eight hours each night had a higher body mass index.

And when the researchers collected blood samples from the volunteers, they discovered that the sleep-deprived had higher levels of ghrelin in their blood. Ghrelin is a hormone produced in the stomach that sends out hunger signals to the brain, which then commands you to be interested in food.

At the same time the sleep-deprived had high levels of hunger-stimulating ghrelin, they had lower levels of leptin. Leptin is another appetite-regulating hormone; it's produced by fat cells and delivers satiation signals to the brain. The particular hormonal ratio of high ghrelin/low leptin was likely encouraging the group to load up on unnecessary calories.

"Before this, people thought obesity was the result of sitting on your butt and stuffing your face," Teheri says. "But it turns out sleep has an influence. It makes sense to me personally, because when I was a sleep-deprived resident, I always had the munchies."

The second study hails from the University of Chicago's sleep laboratory. It shows that sleep loss has an immediate effect on the body's levels of ghrelin and leptin. A few nights of insomnia could thus trick your brain into thinking your body needs more food.

In the sleep lab, a small group of young men were forced to function on four hours of sleep a night for six days. The next year, they returned to the lab, but were allowed a full night's rest for six nights, so that researchers could directly compare their hormone levels and appetite.

During their sleep-deprived week, the men not only showed lower levels of leptin and higher levels of ghrelin, but they also reported stronger cravings for sweet, fatty and salty foods. Sound familiar?

"While there is a lot of attention on diet and exercise [for weight loss], these two studies underscore the importance of adequate sleep," says Terry Young, co-author of Teheri's study and professor of population health sciences at the University of Wisconsin.

"Unfortunately, people think of sleep as an irresponsible activity. It's as if they are being macho, and want to prove how busy and important their lives are. I predict someday that attitude will be as socially unacceptable as smoking."